A typical powder or particle transportation system is shown in FIG. 5. The powder or particle transportation system is connected to a source of powder or particles (not shown) and a plurality of delivery points, such as a plurality of receiving containers or hoppers 20. The transportation system creates a controlled flow of the powder or particles from the source (not shown) to the receiving containers 20. To enable the powder or particles to flow into each container 20, the transportation system usually includes a series of pipe lines 22 and one or more diverter valves 24 connected to the pipe lines 22. Each diverter valve 24 is associated with a respective container 20, e.g., arranged above the respective container 20, so that the powder or particles flow(s) from the diverter valve 24 into the container 20 aided by gravity.
When compressed gas is used to aid in the flow of the powder or particles through the pipe lines and diverter valves, a system for mixing the powder or particles with compressed gas is also provided (not shown).
When used to fill the containers with powder, the diverter valve associated with a first one of the containers is configured to allow the powder to flow from the pipe lines into that container. When that container is filled with powder, the diverter valve associated with that container is reconfigured to stop the supply of powder to the container and to provide a conduit through the diverter valve from a pipe line before the diverter valve to another pipe line after the diverter valve. Then, another diverter valve associated with another, empty container is configured to allow the powder to flow from the pipe lines into that container and powder is thus introduced into that empty container. This process continues, for example, until the containers are filled with powder, after which the containers are removed and empty containers are put in their place.
FIGS. 6-9 show a conventional diverter valve which includes a ball valve having a body casing 13 and a ball disk 12 enclosed in the body casing 13. A curved passage 10 is defined by the ball disk 12. The ball disk 12 is rotated by a stem 12a (see FIG. 7) that projects outward from the body casing 13 and is connected to an operating device such as motor, air actuator or air cylinder (not shown).
The casing of the diverter valve has three branches, namely an inlet branch 15A, a first outlet branch 15B and a secondary outlet branch 15C, all of which are connected to the body casing 13, e.g., by bolts as shown.
The ball valve has two operating positions. In a first operating position shown in FIG. 8, the passage 10 of the ball disk 12 connects the inlet branch 15A and the first outlet branch 15B to thereby provide a first passage through the diverter valve. In a second operating position shown in FIG. 9, which is obtained by turning the ball disk 12 via stem 12A, the passage 10 of the ball disk 12 connects the inlet branch 15A and the secondary outlet branch 15C to provide a second passage which leads to, for example, a receiving container (not shown). By adjusting the position of the ball disk 12, the passage 10 for the powder is changed to provide, for example, either a flow through the diverter valve or a flow into a receiving container.
There are significant drawbacks of such conventional ball valves in diverter valves. For example, when powder flows through a transportation system including a plurality of pipe lines and diverter valves, the powder often passes through several ball valves from the source to a container and impacts an inner wall of each ball valve twice, i.e., at a curve in passage 10 in the ball disk 12 and at a curve in outlet branch 15B or in outlet branch 15C. Such impacts damage the powder. This damage is heightened when there are many valves in each pipe line because the greater number of valves, the greater number of impacts of the powder against the inner walls thereof. When transporting rice, for example, the impact of the rice granules against the walls of the ball valves causes cracking, and since damaged rice is considered a low grade quality, it results in an economical loss.
Similarly, when transporting an adherent powder through the transportation system, such as calcium hydroxide, the powder sticks to the inner walls of the ball valves and causes significant energy loss, and moreover can lead to clogging of one or more of the passages which would result in a complete stoppage of the transportation system.
Another drawback of such conventional diverter valves with ball valves arises from the fact that the interior pressure of the transportation system is higher than atmospheric pressure and to maintain the higher-than-atmospheric pressure in the interior of the transportation system and prevent leakage of air pressure, seal rings are arranged between the ball disk 12 and each of the inlet and outlet branches 15A, 15B, 15C. The tolerance of the deviation of the ball disk from a spherical shape is about 0.02 mm; however, even with special machining by experienced personnel, the tolerance limit is 0.005 mm so that there is invariably leakage of air pressure around the ball disk 12.
Furthermore, when transporting soft powder, a plastic seal ring is used. If the plastic seal ring is too soft, wearing of the seal ring occurs and therefore, the seal ring must have a certain degree of hardness. It is a drawback though that hard seal rings must be forcibly urged against the surface of the ball disk 12 using, for example, elasticity of the plastic material to minimize the leakage. This necessitates a strong force against the ball disk 12 to deform the seal ring and at the same time, a large torque to rotate the ball disk 12. To provide this, a large and expensive operating device is required.
On the other hand, when transporting a very hard powder such as polycarbonate, a plastic seal ring cannot be used because it wears out quite quickly. Metal seal rings are therefore used instead of plastic seal rings, but a major problem with metal seal rings is that the amount of gas leaking through the seal rings is significantly higher than if plastic seal rings are used because the metal seal rings do not have any flexibility. The inability to reduce the clearance between the ball disk and the metal seal ring in view of machining constraints, as described above, also results in gas leakage.